Continuous digester discharger containing automatic temperature and level sensing means and method thereof



July 7, 1970 n. a. SUTHERLAND 3 CONTINUQUS DIGESTER DISCHARGER CONTAINING AUTOMATIC TEMPERATURE AND LEVEL SENSING MEANS AND METHOD THEREOF Filed April 1'7, 1967 2 Sheets-Shed 1" i-TG-l A B i 15 l 10 11 12 k1 *1. 54

l/V VE/V TOR DOUGLAS G. SUTHERLAND A TTORNE Y8 July 1970 D. G. SUTHERLAND 3,519,532

CONTINUOUS DIGESTER DISCHARGER CONTAINING AUTOMATIC TEMPERATURE AND LEVEL SENSING MEANS AND METHOD THEREOF Filed April 17, 1967 2 Sheets-Shee t 2 FIG 5 a? as 85 United States Patent O 3,519,532 CONTINUOUS DIGESTER DISCHARGER CONTAIN ING AUTOMATIC TEMPERATURE AND LEVEL SENSING MEANS AND METHOD THEREOF Douglas G. Sutherland, Middletown, Ohio, assignor to The Black Clawson Company, Hamilton, Ohio, a corporation of Ohio Filed Apr. 17, 1967, Ser. No. 631,291 Int. Cl. D21c 7/08 US. Cl. 16252 4 Claims ABSTRACT OF THE DISCLOSURE A cold blow discharger for use with a continuous digester for wood pulp in the manufacture of paper, which receives the treated wood chips from the digester, reduces the temperature thereof, and expands them through an orifice from where they are transferred to the subsequent steps in the manufacturing process. The discharger utilizes no moving parts, and liquor, at a specific temperature and pressure, is admitted tangentially to the discharger establishing a swirling flow pattern in the discharger, thus maintaining circulation in the discharger while reducing both the temperature of the pulp components and the steam requirements of the system as a whole.

BACKGROUND OF THE INVENTION This invention is an improvement over the system disclosed in Keogh et al. No. 2,616,802, issued Nov. 4, 1952, and Surino No. 2,882,967, issued Apr. 21, 1959, both of which are assigned to the assignee of this invention.

In the processing of wood pulp for the manufacture of paper, continuous digesters are widely used, and the blowing operation for removing the cooked pulp material from the digester must also be a continuous process, one form of continuous discharger being shown in the above Keogh and Surino patents, but the loss of steam through the digester is expensive, and the complexity of the discharge apparatus creates maintenance problems. In addition, when the cooked chips or other pulp materials are blown through the orifice at high temperature of the order existing in the digester, damage to the strength properties of the fibers may occur.

SUMMARY OF THE INVENTION In its preferred form, the process and apparatus is designed for the continuous discharge of pulp material from a continuous digester.

The discharger apparatus in accordance with the invention includes a cylindrical tank mounted vertically for receiving the pressurized cooked pulp or other material as it is continually discharged from the digester or other continuous processing apparatus, and also for receiving a continuous supply of liquid at a substantially lower temperature than exists in the digester. At the base of the housing, a discharge outlet is provided through which the material is discharged as a result of the centrifugal force imparted thereto by the pressure differential between the interior of the tank and the downstream side of the opening. The liquid level, the temperatures, and the pressures within the discharger are precisely controlled by an automatic system. An upstanding spud may be disposed centrally on the bottom wall of the housing as a finder for assuring that circulation is maintained when liquor is injected tangentially into the housing, and the continuous circulation maintains the discharge opening clear of chips since the rotation of the mass continually wipes across the discharge orifice.

3,519,532 Patented July 7, 1970 BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT The system shown in FIG. 1 generally includes a feed zone A and an intermediate or cooking zone B in which the wood chips are cooked and digested so that the ligneous and other non-cellulosic incrustants or binding materials in the wood are softened or removed to render the wood fibers desirably separable for subsequent preparation of the pulp slurry. More particularly, the feed zone A comprises a feed hopper 10 for the wood chips or other forms of ligno-cellulose material which conducts it to a screw feeder 11 rotatably driven in tapered neck-like casing 12.

Saturated steam is supplied to the casing 14 through valved injector pipe 15 for maintaining a regulated superatmospheric pressure and temperature in both the zone B and the discharge zone C for softening the ligneous fibrebinding incrustants. A chemical may be supplied to zone B through valved injection pipe 16 for use in rendering the ligneous binding material water soluble or for other purposes.

A screw conveyor 17 is provided in the casing 14 for the purpose of controlling carefully the rate of progress and the time of transit of the chips through and along the casing 14. Connected near the downstream end of the casing 14 is a downwardly extending discharge pipe 18 through which wood chips from the conduit freely fall through the opening 19. The digester described above 18 substantially identical to that shown in the above patents.

The discharger 20 embodies the present invention and is mounted on the lower end of the down-pipe 18 in communication with the outlet opening 19 of the digester. The discharger 20 includes an elongated tubular tank or housing 21 having a closed base 22 and a radial flange 24 on the upper end thereof which is utilized for interconnection with the similar flange 25 on the down-pipe 18. The inner diameters of the down-pipe 18 and the housing 21 are substantially identical, and the down-pipe can be considered as part of the discharger 20 for operational purposes.

The housing including the side walls 26 and bottom wall 22 has inner surfaces which are relatively smooth, and the bottom wall 22 is additionally arcuate or concave and supports the vertical spud 30. This spud is rigidly secured on the center line of the housing 21, and has a cylindrical section 32 with a conical section 33 provided on the upper end thereof, as shown in FIG. 2.

Upper and lower tangential inlets 35 and 36 are provided in the housing 21 for connection to the cold liquor conduits 38. These inlets charge the discharger 20 with cold liquid at a preset volume rate and pressure, and this liquid enters substantially tangentially to the inner wall 26 of the housing 21. Each of the conduits 38 is provided with a valve 40 controlled by a suitable control system which includes a temperature sensor 41 mounted on the side wall 26 of the discharger 20 for sensing the temperature of the liquid inside the housing 21. The sensor 41 is electrically connected to a transmitter 42 which supplies a suitable signal to the temperature recorder and 3 controller unit 44 which supplies the necessary control to the valve actuator 45 for opening or closing the valves 40, as will be further described.

A discharge valve is provided adjacent the bottom Wall 22 of the discharger 20 for carefully controlling the amount of pulp and liquor discharged under pressure from the discharger into the conduit 52 which leads to the subsequent treatment apparatus 54 (FIG. 1). The discharge valve 50 is shown in FIGS. 46 and includes a housing 55 having the radial flange 56 which is connected by the conventional fasteners 57 to the annular portion 58 of the housing 21 which defines the outlet opening 60 in the side wall 26. A suitable gasket 61 is provided to insure fluid tight engagement therebetween.

The housing 55 has the inner tubular sleeve 62 secured thereto to define the outlet passage 63 therethrough. A disk-shaped plate 64 is fixed to the left-hand end of the valve housing 55 and has a discharge opening 66 therein in communication with the passage 63. The fixed shutter member 68 is secured to the plate 64 below the opening 66 for cooperation with the movable shutter 70 to block completely flow through the opening 66 when the adjacent surfaces 71-72 and 73-74 are in contact.

The actuator shaft 75 supports the movable shutter 70 which is fixedly mounted on shaft 75 and rocks back and forth with rotation of the shaft to restrict or open the discharge opening 66. This actuator shaft extends through the packing member 77 and has its opposite end 78 pivotally supported in the radial flange 79 on the tubular housing 55. An actuator 80 is provided on the lower portion of the valve housing 55 to extend the actuator lever 83, which is fixed to shaft 75, between the alternate positions shown in FIG. 4 to move the shutter 70 by rotation of the actuator shaft 78. A suitable control unit is provided adjacent the actuator 80 for controlling the operation of this actuator. Specifically, the control unit includes a valve (not shown) whose position is precisely positioned, and the follow-up arm 86 is provided to sense the movement of the yoke 87 on the end of the piston rod 88 of the actuator 80 and terminate movement of the piston rod when the proper position of the shutter 70 is attained.

The control system 85 for the discharge valve 50 responds to the liquid level within the discharger housing 21 as determined by the level sensing device 90 mounted on the side wall 26 of the housing and electrically connected through the level transmitter 91 to the level indicator controller 92. The latter is connected to the control unit 85 to supply the necessary signal to open and close the valve 50 so that a preset level of liquid is maintained in the housing 21.

In operation, the discharger 20 receives treated pulp from the digester through the opening 19. The interior of the discharger is pressurized by the steam present in the digester so that the pulp is at an elevated pressure and temperature as it falls into the discharger. Liquor at a predetermined temperature is continuously supplied to the housing by pumping it through the tangential inlets 35 and 36 so that it creates a rotating mass of liquor about the spud 32 which tends to stabilize the circulation. The liquor then passes through the discharge opening 66 into the conduit 52 which is at a substantially reduced pressure. The level of liquor in the housing 21 is automatically controlled by the level sensor 90 which cooperates with the control system 85 and actuator 80 to vary the size of the discharge opening 66 thereby regulating the rate of flow from the tank.

Similarly, the temperature of the rotating liquor is maintained within prescribed limits by the sensor 41 and control 44 which position the valves 40 to increase or decrease appropriately the liquor being fed into the housing 21. The temperature and level sensing systems thus are interrelated since an increase in temperature would increase the flow through the inlets 35 and 36, and thus the level within the housing 21 would be compensated for by increasing the size of the discharge orifice.

As the hot treated pulp leaves the digester, it falls freely through the upper portion of the discharger until it contacts the rotating mass of liquor. Centrifugal force tends to move the pulp particles outwardly adjacent the inner surface 26 of the housing 21, and gravity tends to draw them downwardly so that the particles eventually rotate past the discharge opening 66 through which they are expelled. There exists a substantial pressure differential on either side of the opening 66 which causes the pulp particles to be expanded as they pass through the orifice thereby further separating the individual cellulose fibers. Since the liquor is maintained at a temperature substantially less than the temperature of the pulp material as it leaves the digester, the pulp material is cooled to maintain a temperature below that at which serious mechanical damage to the fibers could occur.

In the preferred embodiment of the discharger 20, the housing has an inner diameter of about 27 inches and a vertical height between the flange 24 and the bottom wall 22 of about 5 feet with the spud 32 having a diameter of about 9 inches. The control system is calibrated to maintain the level of liquor within the housing so that there is a free fall from the digester of about 6 to 24 inches. The pulp leaves the digester with a consistency of about 20% solids at about 385 F., and falls into the liquor which is being supplied through the tangential inlets 35 and 36 at 20-30 feet per second at a temperature of about 180 F. and creates a consistency of about 4-10% solids. This effects a whirling motion which is stabilized by the vertical spud 30 and the centrifugal force in the swirling mass forcing the heavier particles outwardly against the inner wall 21 of the housing 20. The discharge valve 50 allows controlled ejection of the pulp particles through the opening 66 and discharges the pulp into the conduit 52 at a temperature of about 240 F., Well below the 385 F. temperature at which it left the digester.

While the spud 32 is shown and described as having a particular configuration, it is within the scope of the invention to use different sizes and configurations thereof to stabilize the circulation. In some instances, it is possible to eliminate the spud completely. Moreover, the discharger can be used With other types of continuous digesters and processing equipment, and the particular discharge valve shown and described herein can be modified without departing from the scope of the invention.

The invention has thus provided a method and apparatus for discharging a material from continuous processing equipment without the use of moving parts within the discharge apparatus except for a discharge control valve. While the apparatus and method are suitiable for the cold blowing of wood pulp from a continuous digester, the invention is not necessarily limited to this application.

While the method and form of apparatus herein described constitute preferred embodiments of the invention, it is to be understood that the invention is not limited to this precise method and form of apparatus, and that changes may be made therein without departing from the scope of the invention which is defined in the appended claims.

What is claimed is:

1. In combination with a digester discharging paper making pulp on a substantially continuous basis and a substantially vertically extending discharge pipe extending from the downstream end of said digester the improvement comprising:

(a) a tank mounted on the downstream end of said discharge pipe to receive said pulp from said digester,

(b) said tank having a side wall and means defining with said side wall a stationary, substantially annular channel in said tank,

(c) means for introducing a cooling liquid into said tank substantially tangentially with respect to said channel to establish a swirling flow pattern in said tank through said tangential introduction of liquid to intermix said pulp and liquid and maintain the discharge opening from said tank unobstructed by the contents thereof,

((1) means for sensing the temperature of the contents of said tank,

(e) means responsive to said temperature sensing means for controlling the flow rate of said cooling liquid into said tank,

(f) an adjustable valve mounted in said tank adjacent the base thereof,

(g) means for sensing the level of the contents of said tank, and

(h) means responsive to said level sensing means for controlling the adjustment of said valve.

2. The improvement of claim 1 wherein:

(a) said tank side wall is substantially cylindrical, and

(b) said means defining with said side wall an annular channel comprises a substantially cylindrical spud positioned in said tank substantially concentrically with respect to the side wall thereof.

3. A method of discharging the contents of a continuous digester comprising:

(a) discharging pulp at a first temperature from said digester into a discharge tank having a substantially cylindrical side wall,

(b) introducing liquid into said tank,

(i) at a temperature substantially lower than said first temperature, and

(ii) substantially tangentially with respect to said side wall to establish a swirling flow pattern in said tank through said tangential introduction of liquid to intermix said pulp and liquid and maintain the discharge opening from said tank unobstructed by the contents thereof,

(c) monitoring the temperature of the mixed pulp and liquid,

(d) controlling the flow rate of said liquid into said tank in response to said temperature of said mixed pulp and liquid, and

(e) discharging said mixed pulp and liquid from said tank.

4. The method of claim 3 further comprising:

(a) monitoring the total amount of pulp and liquid in said tank, and

(b) controlling the rate of discharge of said mixed pulp and liquid from said tank in response to the amount of pulp and liquid in said tank.

References Cited UNITED STATES PATENTS 1,776,761 9/1930 Morterud 16252 X 2,882,967 4/1959 Surino 162246 2,938,824 5/1960 Richter 162-246 X 3,041,233 6/1962 Richter 16252 X 3,206,356 9/1965 Carlsmith 162237 S. LEON BASHORE, Primary Examiner A. L. CORBIN, Assistant Examiner US. Cl. X.R. 

